I've long held an unsupported belief that life anywhere in any form would "converge" upon only a few interesting things left to do after having mastered rearranging atoms and forces in any configuration they desire.

Not only is there likely an ideal, optimized way of sending information long distances, I suspect there also a very limited number of things a matrioshka brain would care to broadcast or receive, like the values of some fundamental constant.

Saying "hi" for fun to other civilizations isn't even something we do on our own planet with our own people. We only talk to people for specific reasons, even if we're unaware of those reasons. We'll go out of our way to avoid a homeless person's greeting rather than risk learning something about/from him.